Bridging Device

ABSTRACT

A bridging device ( 10 ) for providing a bridging surface ( 12 ) between two points comprising a stack of interjoined beams ( 14 ) housed in a retracted position in a housing ( 11 ) mounted at a first point; and a drive system that drives the beams ( 14 ) to slide one over the other to telescopically extend out of the housing ( 11 ) from the retracted position to an extended position to thereby form a bridging surface ( 12 ) to a second point.

BACKGROUND OF THE INVENTION

Automated access ramps and other bridging devices bridge gaps andprovide a pathway for persons or vehicles to cross.

Automatic ramps are very useful in the public and private transportindustry. The ramps allow access onto and off trains and road vehiclesfor both enabled and disabled commuters as well as small vehicles suchas bicycles and factor handling vehicles.

Known automatic ramps have several inherent problems. Firstly, in theirretracted state they are bulky and require a large area to mount. Someof them-are also heavy which is undesirable in terms of speed and fuelefficiency if the retractable ramp is mounted on a transport vehicle.The aerodynamics and weight balance of vehicles can be affected bymounting a ramp structure to the vehicle. Most automated access ramps,due to their size, are economically unviable for retrofitting toexisting transport systems. Retrofitting is made more difficult by thevarious structural constraints associated with mounting the ramps.Additionally, most devices need to be fully extended to perform thefunction of a ramp and can be unwieldy if the gap to be bridged issmall.

WO 99/52738 describes an articulated ramp which is an earlier ramp bythe inventors of the present invention. The ramp assembly describedtherein comprises a plurality of articulated segments forming a rampbody that extends from a retracted position located below the surface ofthe vehicle to an extended position where it bridges a gap between thevehicle and a second surface. The housing for the ramp body locatesunder the vehicle and houses the length of the ramp body in asubstantially vertical position. Accordingly, the ramp body must becapable of significant curving through approximately 90° to achieve itsfinal extended position. This articulated ramp assembly is awkward andvery bulky, particularly when it is attached below the carriage floor ofa train where space below the floor is limited and the aerodynamics andweight balance of the train could be affected by such a structuremounted to the carriages.

Furthermore, the articulated segments forming the ramp body of WO99/52738 move in a scissor and clamping motion which present safetyproblems to the operator and the public. This scissor and clampingmotion easily runs the risk of rendering the function of the rampinoperable by the invasion of foreign objects, by accident or sabotage.This could result in disruption to transport schedules and possiblephysical injury.

The present bridging device addresses these drawbacks and the drawbackswith other known bridging devices.

SUMMARY OF THE INVENTION

In one aspect of the invention there is a bridging device that providesa bridging surface between two points and comprises:

a stack of interjoined beams housed in a retracted position in a housingmounted at a first point; and

a drive system that drives the beams to slide one over the other totelescopically extend out of the housing from the retracted position toan extended position thereby forming a bridging surface to a secondpoint.

Preferably, the beams are of a flat, slat-like form and are supported byend plates located at each end. The beams may have a forward edge thatis downturned at an angle. The end plates are each stacked adjacent eachother and slidingly engage the end plates on each adjacent side toenable telescopic movement of the bridging device.

The sliding engagement of the end plates is preferably effected by asliding boss and key slot engagement which limits the extent thatadjacent end plates may slide relative to one another. The underside ofeach end plate is preferably provided with a gear rack that meshes witha drive gear on a drive shaft that is driven by a drive source in thedrive system.

Preferably, each end plate meshes with a drive gear dedicated to thatend plate. The drive gears corresponding to each end plate areco-axially mounted on the drive shaft and clustered towards both ends ofthe drive shaft.

The drive shaft is preferably bearing mounted on the housing and isdriven by a motor in the drive system, which is also mounted in thehousing.

The first plate, which is the leading plate when the stack of beams isextended, is preferably provided with a wheel to allow the leading endof the bridging surface to move with the extending bridge when theleading end contacts the ground.

Each end plate preferably has a lock to lock adjacent plates in theextended position and prevent unintentional retraction.

In one embodiment the lock is a pivoting lever pinned in a recess on theend plate and adjacent the key slot on the same end plate, through whicha boss on an adjacent plate protrudes. The lever pivots to protrude intothe key slot and obstruct the boss from sliding out of the extendedposition.

The pivoting lever preferably has two tabs. The corresponding drive gearcontacts the first tab as the bridging device is extending therebymoving the lock into a locked position. The drive gear contacts thesecond tab when moving to retract the bridging device thereby moving thelock into an unlocked position and allowing the end plates to retractback into the housing.

The key slot is preferably angled at a rear end to create a curve to theend plates when extended, therefore giving the bridging device in itsextended position a pre-camber for visual appeal and psychologicalreassurance of its strength.

The housing is preferably an enclosed elongated structure having a frontopening through which the beams extend. The opening may be provided witha tilting sprung cover. The sides of the opening may be provided withside shutters to cover the partially exposed opening. When in theextended position the beam located at the opening does not extend acrossthe entire width of the opening.

The housing may be provided with base-mounted springs under the stack ofbeams to give an upward force to assist the incremental rise of thestack during extension.

The housing may further be provided with an end pull for stabilising thelast plates supporting the last beam in the stack, which remainsstationary inside the housing. When in the extended position the lastplates inherently tend to tilt upwards. Accordingly, the end pull pullsthe leading edge of the last plates downwards.

The end pull preferably comprises a tension spring located horizontallybetween the last pair of end plates and a tether attached to each end ofthe spring which extends in opposite directions, and turned through 90°around guide rollers to extend upwards and attach to, or close to, therespective last end plates.

The stack of beams is preferably restrained at the front of the housingin cassette form, only allowing the top beam to progress over catches ontop of the restrainer as the stack of beams rises incrementally. Thecatches are biased by suitable biasing means such as sprung balls or asingle leaf spring.

The interjoined beams may be of different lengths so as to create atrapezium shaped surface, or other shaped surface. The beams arepreferably supported on top of the end plates but they may be supportedunderneath the end plates such that the end plates protrude upwards andform a border along the sides of the bridging surface.

The housing may be mounted in a tilting position to vary the angle atwhich the bridging surface extends. The tilting angle may beautomatically or manually controlled to vary. A sensor may be providedto sense the required angle of tilt so that the angle may be adjustedaccordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described further by way of example withreference to the accompanying drawings by which:

FIGS. 1( a), 1(b) and 1(c) illustrate applications of a bridging deviceaccording to the present invention;

FIG. 2 is a perspective view of a bridging device according to thepresent invention in an extended position;

FIGS. 3( a), 3(b) and 3(c) illustrate the bridging device in a retractedposition, a partially extended position and a fully extended positionrespectively bridging a gap between points of different heights;

FIG. 3( d) illustrates the bridging device partially extended betweenpoints of the same height;

FIG. 4( a) is a perspective view of the bridging device in a retractedposition;

FIG. 4( b) is a view similar to FIG. 4( a) but shows the retracted beamslocated inside the housing;

FIG. 4( c) is a view similar to FIG. 4( a) but illustrates the drivingmechanism located inside the housing;

FIG. 4( d) is a view similar to FIG. 4( a) but illustrates various othercomponents located inside the housing;

FIG. 5 is a part front view of one end of the extendable beams of thebridging device;

FIG. 6 is a side view of FIG. 5 viewed from the section A-A;

FIGS. 7( a), 7(b) and 7(c) illustrate in three sequential steps themechanics and movement of an end plate as it is driven into the extendedposition;

FIG. 8 illustrates one embodiment of a lock of the bridging device;

FIG. 9 is a perspective illustration of the last plates located in thebridging device;

FIG. 10 is a side sectional view taken at section B-B of FIG. 9;

FIG. 11 is a front view of an end of a stack of beams according toanother embodiment of the bridging device; and

FIG. 12 is a front view of an end of the stack of beams in accordancewith yet another embodiment of the bridging device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The Figures illustrate a bridging device 10 that in its preferred use isadapted to be mounted at or under a door opening of a vehicle. Such avehicle could be a train, tram, bus, taxi, water vehicles such asferries, or private road vehicles.

The bridging device 10 comprises a housing 11 from which, as illustratedin FIG. 2, a bridging surface, or ramp 12, telescopically extends. Theramp 12 is designed to bridge a gap between two points and specificallybetween the point at which the housing 11 is mounted and a point at theopposite side of the gap. Furthermore, the gap may be between: twospaced surfaces at the same level or surfaces of uneven height. Aleading edge 13 of the ramp may be supported on the opposite surface ormay remain unsupported, extending in a cantilevered fashion from thehousing.

The ramp 12 comprises a stack of interjoined beams 14 that slide out ofthe housing one over the other to telescopically extend from theretracted position, as illustrated in FIGS. 3( a) and 6, through thepartial extension of FIG. 3( b) and to a fully extended position asillustrated in FIG. 3( c) where the leading edge 13 is supported on thelower surface on the opposite side of a gap. The extended ramp is stableand capable of holding sufficient loads and withstand the normal loadsassociated with a crowd of people including wheelchairs, exiting publictransport, or the weight of a vehicle traversing a gap.

FIG. 3( d) illustrates an alternative situation where the bridgingdevice extends to bridge a small gap between level surfaces. Here theramp only needs to extend part-way to close the gap without the leadingedge of the ramp having to rest on the opposite surface. This can beachieved because the ramp 12 of the bridging device can extend as acantilever and remain in an extended position entirely unsupported atits leading edge. This is achieved as a result of the structure ofinterjoining beams which provide strength to the ramp when partially orfully extended. Accordingly, the bridging device 10 can be used as aramp between uneven surfaces where the leading edge rests on theopposite surface, or used as a bridge between surfaces, typically evensurfaces, where the leading edge is not supported but is aligned levelwith the opposite surface as illustrated in FIG. 3( d).

The interjoined beams 14 are made of a strong, stiff material andoverlap one another to prevent buckling of the ramp under high loads.

Housing 11 is a rectangular box structure that houses all the maincomponents of the bridging device and is significantly smaller than thehousing structures of known bridging devices.

Housing 11 is all enclosed, as illustrated in FIG. 4( a), but for anopening 15 on its front face through which the ramp extends. When in theretracted position the opening is closed by hinged cover 16.

FIG. 4( b) illustrates the stacked beams 14 in a retracted positioninside the housing 11.

FIG. 4( c) illustrates the driving mechanism 20 used to drive the beamsto automatically extend into a ramp.

FIG. 4( d) illustrates sliding shutters 21 which serve to close theexposed portion of opening 15 when the extended ramp does not entirelyfill the opening 15. FIG. 2, for example, illustrates the ramp in theextended position. Owing to the telescopic nature of the bridgingdevice, the first beam 22 at the leading edge 13 is longer than the lastbeam 23, with all the beams in-between graduated in length from thefirst beam 22 to the last beam 23. Consequently there remains a gap inthe opening 15 through which particles and objects could enter anddamage the device 10. Accordingly, the sliding shutters 21 slide inguides 24 from the side of the housing to the front to close off theopening. The shutters may be driven from the main gear drive via cablesand pulleys, thereby synchronizing the shutters' movement with that ofthe beams. Alternatively, the shutters may be spring loaded to shut asthe ramp 12 extends.

FIG. 4( d) also illustrates vertical track brackets 25 mounted in thehousing 11 that restrain the last beam 23 in the stack stationary insidethe housing and form a vertical track inside the housing allowingvertical movement only.

The ramp 12 comprises beams, of a flat slat-like construction,overlapping one another. Each beam 14 is supported at both ends by anelongated end plate 30. In the preferred embodiment the beam issupported perpendicularly to the end plate and on top of the end plate.In the retracted position when all the beams 14 are stacked one on topof the other, the end plates are stacked one adjacent to the other. Thisarrangement is illustrated in FIGS. 5 and 6.

Each end plate slidingly engages the end plates on each adjacent sidethereby enabling telescopic movement of the bridging device 10. Theleading pair of end plates 31 at the leading edge 13 of the ramp and thelast pair of end plates 33 in the housing 11 obviously only engage oneother end plate. Additionally, the last pair of end plates 33 are fixedto the housing by way of brackets 25.

To make it possible for the beams to extend out onto a continuous levelsurface, the beams are graduated in length so as to accommodate the endplates 30 (see FIG. 5, for example). Hence, the leading edge 13 end ofthe ramp is wider than the housing end in this embodiment.

The leading pair of plates 31 at the leading end of the ramp areprovided with a wheel 32. The wheel 32 is the first point of contact ona surface as the ramp extends to the surface. It enables the ramp tosmoothly move along the surface as it extends.

The bridging device 10 may be designed to only extend partway if it isnot necessary to execute a full extension or if an obstruction isencountered. In this case sensors are used to prevent contact betweenthe leading end of the ramp and an obstruction.

FIGS. 7( a) to 7(c) illustrate the mechanics of the end plates 30 thatenable each end plate to slide against an adjacent end plate to providethe telescopic extension of the ramp.

Adjacent end plates slidingly engage by a slide boss and slotengagement. The inner face 34 of each end plate 30 has a slot 35. Theouter face 36 of each end plate is provided with two bosses 37, oralternatively a single, elongated boss, which engage the slot 35 of anadjacent end plate. The slot has closed ends thereby preventing thebosses from escaping and adjacent plates from detaching. The spacingbetween the bosses is such that in the extreme positions in the slot 35the beams 14 supported by the end plates are either stacked one abovethe other or extended still with some overlap without gaps therebetween.

In another embodiment the tolerance between the key slot and boss may beincreased. This results in an extended ramp that drops slightly undergravity, which is useful where the first surface to which the bridgingdevice is mounted is higher than the second surface across a gap. Ineffect the ramp ‘seeks’ the opposite second surface as it extendsdownward.

The beams 14 themselves may have a downturned edge 64 at the front edge,which provides additional strength for lighter weight, larger spans andstiffer construction. This is best seen in FIGS. 7( a), 7(b) and 7(c).The downturned edge 64 on each beam is angled forward to allow the beamsto be stacked substantially vertically. In the extended position thedownturned edge 64 of a beam is located underneath the rear edge of thebeam in front. Therefore, each beam rests on the beam behind it as shownin FIG. 7( c), which increases the strength of the ramp.

A gear rack 40 is located in a recess 41 along the bottom edge of eachplate and is flush with the inner face 34 of the plate. The gear rack 40meshes with a drive gear 42 axially mounted on a drive shaft 43. Thegear rack 40 bends upwards at the leading end to allow smooth meshing ofthe different level racks onto the gears thereby catering for the leadin between each plate due to the difference in stack height. Apredetermined rise allows sufficient clearance for adjacent plate racksto mesh with the gears. This rise is preferably about 4 mm.

Drive shaft 43 is mounted in the housing on bearings and is driven bydriving mechanism 20 that, as illustrated in FIG. 4( c), essentiallycomprises a motor 50, gear box 51 and a flexible or solid drive shaft 52that drives drive shaft 43. All the components of the drive mechanismare mounted in the housing in the configuration of this particularembodiment.

Each gear rack 40 on each plate engages only with its own correspondingdrive gear 42 such that each plate has its own gearing system.Accordingly, and as illustrated in FIG. 4( c), the drive shaft 43supports a number of co-axially mounted drive gears 42 that eachcorrespond to an end plate 30. In this configuration the drive gears 42are clustered at each end of the drive shaft 43 and operate in pairs tocorrespond with each pair of end plates 30 mounted to every beam 14.Accordingly, each drive gear 42 on one side of the drive shaft 43 has acorresponding pair located at the other end of the drive shaft.

By virtue of the end plates 30 at each end, the beams 14 sequentiallyslide over each other to telescopically extend into a ramp. In thisembodiment extension begins with the top most beam, which is the firstand forward most beam. In the first instance the drive shaft 43 alignsthe first pair of drive gears, located at the extreme far ends of thedrive shaft 43, with the leading pair of end plates 31 supporting thefirst beam 22 to extend out of the housing.

Turning back to FIGS. 7( a) to 7(c) the drive shaft 43 rotates drivegear 42 to engage rack 40 of a first pair of end plates 30 a and todrive the end plates, and consequentially the beam 14, in a forwarddirection. FIG. 7( b) illustrates gear 42 moving end plate 30 a in aforward direction to reach the position illustrated in FIG. 7( c). Asgear 42 passes the point illustrated in FIG. 7( c), bosses 37 of asecond plate 30 b (illustrated in ghost lines) located in the slot 35 ofthe first plate 30 a do not allow the first plate 30 a to travel anyfurther without pulling the second plate 30 b along with it.

The leading end plates 31 are longer than the remaining end plates sothat the gear racks on the leading plates can remain engaged with thedrive gears while the ramp is in the retracted position. FIG. 6 bestillustrates this.

At this point the driving force is transferred from the gear rack 40 ofthe first plate 30 a to the adjacent drive gear associated with thesecond end plate 30 b. The second drive gear corresponding to the secondend plate 30 b is not illustrated in FIGS. 7( a) to 7(c) but would belocated in front of the first drive gear 42 as viewed in those Figures.

The second drive gear would then rotationally engage with the second endplates gear rack (not shown) to drive the second plate 30 b forwarduntil the bosses 37 in the third end plate 30 c (illustrated in ghostlines) engage with the rear end of the slot of the second end plate.

The driving process thus continues by sequentially transferring thedriving force from one drive gear 42 to the next.

The driving mechanism 20 stops when the drive shaft has moved forwardthe second last end plate. The last end plate is fixed and remainsstationery.

To ensure each end plate remains in a forward position relative to theend plate immediately behind it, each end plate is provided with a lock.

FIGS. 7( a), 7(b), 7(c) and 8 illustrate one embodiment of lock in whichthe lock is a lever plate 45 pivotingly mounted on inner face 34 withpin 44. Lever 45 is pinned to the inner face 34 of each end plate 30 ina corresponding recess 46. Specifically, the lever 45 is positioned oninner face 34 between slot 35 and gear rack 40 so that pivoting movementof the lever causes it to protrude into slot 35 and interfere with rack40.

FIGS. 7( a) and 7(b) illustrate the lever 45 in an unlocked orientation.FIG. 7( c) illustrates the lever 45 rotated in a clockwise direction toprotrude into slot 35 to thereby confine bosses 37 towards the rear ofslot 35 and lock the adjacent plates in an extended position.

Lever 45 is pivoted into the locked position by drive gear 42 rotatingalong gear rack 40. Lever 45 has two tabs extending downwardly adjacentgear rack 40. These are: lock tab 47 and unlock tab 48.

As drive gear 42 rotates in the direction extending the ramp, the drivegear passes under unlock tab 48, which is shorter than lock tab 47, andcontacts lock tab 47. This contact occurs when the slot 35 of the firstend plate 30 a has moved forward such that bosses 37 of the second endplate 30 b reach the rear of slots 35. This is illustrated in FIG. 7(c). At this point the contact between the drive gear 42 and lever 45pivots the lever in a clockwise direction to protrude into slot 35 andprevent bosses 37 moving from the rear of slot 35.

As the drive shaft and drive gears systematically move from one pair ofplates to the next, each end plate is locked against the end platebehind it. The result is an extended ramp that can be securely andstably used without the concern that the plates could slide back overeach other and the ramp collapse.

When retracting the beams 14 the drive shaft rotates in the oppositedirection to systematically retract each beam one by one beginning withdriving the second last beam onto the last stationery end plate 33. Inthe retracting position the drive shaft and drive gears rotateanti-clockwise to travel from the position illustrated in FIG. 7( c) tothe position illustrated in FIG. 7( b) then FIG. 7( a). With the lever45 still in the locked position gear 42 travels under lock tab 47 androtates to make contact with unlock tab 48. When contact is made lever45 pivots about pin 44 in an anti-clockwise direction to bring the leverout of the locking position and free bosses 37 to move towards the frontof slot 35 as the end plate 30 is pulled back by the driving mechanism20. Hence, each pair of plates is one by one retracted back into thehousing until the plates adopt the retracted stack position illustratedin FIGS. 5 and 6.

Other embodiments of plate locks may also be used. For example insteadof a lever a spring biased pin may be seated in a stepped apertureextending through each end plate. When extension occurs the pin could beforced to extend to behind the plate adjacent to it and prevent theplate from retracting.

The rear of each slot can be bent or curved to induce a pre-cambercausing the extended ramp 12 to curve slightly and form a hump givingthe structure a sense of stability. In the case of its application as apedestrian walk way, pedestrians are more likely to view the bridgingdevice 10 as a safe and stable ramp to traverse if the ramp has a slightoutward curvature compared with a “sagging” inward curving ramp.

If the bridging device 10 is intended to bridge a gap between two pointshaving relative uneven heights the curve of the extending ramp can beadjusted such that, for example, the telescopically extending rampextends horizontally from the housing and curves to meet a surface thatis lower than the height of the housing. This adjustment can be made byenlarging the bottom rear of slot 35 to form a trajectory curve angle57. The severity of the trajectory curve angle 57 may be varied toachieve the desired curvature through which the bridging device 10telescopically extends.

Alternatively or in combination, the angle of extension can be varied bytilting the entire housing itself relative to its mounting point. Thisallows the ramp to automatically find the correct level of the landingsurface. Should upward tilting be required for situations where thelanding surface is higher, a separate driving mechanism can beincorporated. The bridging device may even be able to sense thenecessary degree of tilt by using a sensor to detect the oppositesurface and adjust the tilt accordingly.

Alternatively, the bridging device may be associated with amicroprocessor which can be pre-programmed to tilt the housing accordingto a pre-programmed location. For example, a bridging device mounted ona train could be programmed to tilt at a specific angle as the trainarrives at a particular station.

For example, if the bridging device 10 is mounted underneath the doorwayentrance of a commuter train the tilt angle of the housing can adjust tothe angle required to bridge the relative height of the platforms andtrain floor. This is useful for accommodating different platform heightscommuters must negotiate when travelling by trains.

To prevent the plates from slipping out over each other under the effectof gravity or friction a stack restrainer 38 at the front of the housingapplies pressure onto the stack so to catch against any slipping beams.The stack restrainer 38 is illustrated in FIGS. 3( a) to 3(c) and FIG.6. The restrainer may be a member attached to the housing having aspring-biased ball, preferably stainless steel, located in a recess atthe top of the member. As the stack rises incrementally the restrainerallows only the top beam in the cassette to depress the sprung ball andpass over.

Alternatively, FIG. 6 illustrates a restrainer 38 in the form of amember having an upper end shaped as a leaf spring which will depress toallow the top most beam to pass over and out of the opening.

The last beam 14 that remains stationery inside the housing is in theform of a more stable brace angle 60 as illustrated in FIG. 10. The endplates 30 on either side of the brace angle 60 are fixed to the housingby way of vertical track brackets 25.

Springs 63 are mounted under the last beam 14 to assist in the stackrising evenly in the cassette (see FIGS. 9 and 10).

In one embodiment of the bridging device there may be a need forassistance in keeping the stack of beams level during extension. In thiscase, an end pull is used to force the nose of the last plates 30downwards. As shown in FIGS. 9 and 10 the end pull comprises a tensionspring 26 located horizontally between the last pair of end plates 30. Atether 27 is attached to each end of the string and extends in oppositedirections towards the end plates 30. Tethers 27 are turned through 90°by rollers 28 so as to extend upward towards their respective end plates30. The ends of tethers 27 are connected to brace angle 60 close to theend plates 30 by means of a pin. This is illustrated in FIG. 10. Thetension force of spring 26 pulls the tethers 27 in a downward directionto react against the tendency of the last pair of plates to pullupwards.

While an end pull is illustrated in FIGS. 9 and 10, it is understoodthat the components of the end pull (spring 26, tethers 27 and rollers28) may be omitted from the bridging device where an end pull is notrequired.

The last end plates themselves are restrained horizontally in thehousing and are provided with limited vertical movement for raising thestack of beams. Vertical restraint is effected by guide wheels 61 andslide guide wheels 62 which enable the last end plates 30 to slide onthe vertical track brackets 25. Alternatively, other vertical slidingmeans, such as bearing tracks, may be used.

The bridging device may be usefully applied to a range of applicationsfrom small scale pedestrian ramps to larger scale bridges for vehicleswhere a temporary bridge is required.

Whilst in the extended position, in this embodiment the ramp inherentlyacquires a trapezoid shape (on account of the first beam being longerthan the last beam). This shape may be exaggerated to give the ramp aflared trapezium shape, which may be desirable in certain applications.

It is possible to construct the bridging device 10 to achieve a straightrectangular ramp with parallel sides. In this case the end plates wouldbe angled inwards as illustrated in FIG. 11. The mechanics of each endplate would be different to that described above, for example bosses maybe replaced with a dove tail key, but the working concept would remainthe same.

In another embodiment illustrated in FIG. 12 rather than mounting thebeams on top of the end plates as illustrated in the preferredembodiment, the beams may be upturned with the end plates projectingupwards. When the bridging device is in an extended position in thisembodiment, it gives the ramp borders along the edges of the ramp andreduces the likelihood of wheel chairs, prams, and the like falling offthe side of the ramp before reaching the end.

The bridging device may be made entirely of metal and foreseeably ofhigh strength steel, or high strength aluminium or cast metal or thelike. Alternatively, the device may involve composite materials made ofcarbon fibres or plastics. It is an advantage to choose high strengthbut lightweight materials to reduce the weight of the bridging deviceand overall vehicle load. When in the retracted position, the bridgingdevice allows a large ramp to be stored in a small space, which isdesirable.

It will be understood to persons skilled in the art of the inventionthat many modifications may be made without departing from the spiritand scope of the invention.

1-40. (canceled)
 41. A bridging device for providing a bridging surfacebetween two points comprising: a housing mountable to a first point; atleast two interjoined beams housed in a retracted position in saidhousing; and a drive system adapted to drive said beams to slide oneover the other to telescopically extend out of said housing from theretracted position to an extended position to thereby form a bridgingsurface to a second point.
 42. The bridging device as set forth in claim41, wherein said beams are supported by end plates located at each endof said beam, said end plates being adapted to be stacked adjacent toeach other and to slidingly engage said end plates on each adjacentside, and wherein said end plates slide relative to one another by wayof a boss and key slot sliding engagement between adjacent end plates.43. The bridging device as set forth in claim 42, wherein an undersideof each end plate is provided with a gear rack that meshes with a drivegear on a drive shaft driven by a drive source in said drive system, andwherein each end plate meshes with its own dedicated drive gearcoaxially mounted on said drive shaft.
 44. The bridging device as setforth in claim 43, wherein said drive shaft is bearing mounted in saidhousing and is driven by a motor defining said drive source.
 45. Thebridging device as set forth in claim 43, wherein each end plate isprovided with a lock to lock adjacent plates in the extended position,wherein said lock is a pivoting lever pinned in a recess on said endplate and adjacent a key slot on said same end plate, through which aboss on said adjacent end plate protrudes, whereby said lever pivots toprotrude into said key slot and obstruct said boss from sliding alongsaid key slot.
 46. The bridging device as set forth in claim 45, whereinsaid pivoting lever is provided at least two tabs, whereby duringextension of said bridging device said drive gear contacts a first tabto move said lock into a locked position, and during retraction of saidbridging device said drive gear contacts a second tab to move said lockinto an unlocked position thereby allowing said end plates and beams toretract back into said housing.
 47. The bridging device as set forth inclaim 45, wherein said key slot is angled at a rear end to create acurve such that when said end plates are in an extended position thebridging surface is cambered.
 48. The bridging device as set forth inclaim 41, wherein said beams are substantially flat and slat-like inshape so as to stack one on top of the other, and having a forward edgethat is downturned at an angle, and wherein said end plates at a leadingfront beam are defined as first plates and are each provided with awheel adapted to contact a surface at the second point.
 49. The bridgingdevice as set forth in claim 48, wherein said beams are made from amaterial selected from the group consisting of metal, compositematerials, carbon fibers, and plastics.
 50. The bridging device as setforth in claim 41, wherein said housing is an enclosed elongatedstructure defining a front opening through which said beams extend, saidopening is provided with a tilting sprung cover.
 51. The bridging deviceas set forth in claim 41 further comprising a biasing means mountable insaid housing to provide an upward force on said beams for incrementallyraising said beams during extension.
 52. The bridging device as setforth in claim 51 further comprising a restraining catch at the front ofsaid housing, said catch being adapted to permit only the top-most beamof said rising beams to extend through said housing during extension.53. A bridging device comprising: a housing mountable to a first point,said housing being an enclosed elongated structure defining a frontopening and including a biased tilting cover; a stack of interjoinedbeams housed in a retracted position in said housing, said beams beingsupported by end plates located at each end of said beams, said endplates being adapted to be stacked adjacent to each other and toslidingly engage said end plates on each adjacent side, wherein said endplates slide relative to one another by way of a boss and key slotsliding engagement between adjacent end plates; a lock provided witheach of said end plates to lock adjacent plates in the extendedposition, each of said locks is a pivoting lever pinned in a recess onsaid end plate and adjacent a key slot on said same end plate, throughwhich a boss on said adjacent end plate protrudes, whereby said leverpivots to protrude into said key slot and obstruct said boss fromsliding along said key slot; and a drive system adapted to drive saidbeams to slide one over the other to telescopically extend out of saidhousing from the retracted position to an extended position to therebyform a bridging surface to a second point, said drive system having amotor; wherein said housing further comprising a biasing means mountabletherein and a restraining catch located at the front of said housing,said biasing means being adapted to provide an upward force on saidbeams for incrementally raising said beams during extension, saidrestraining catch being adapted to permit only the top-most beam of saidrising beams to extend through said housing during extension; wherein anunderside of each end plate is provided with a gear rack that mesheswith a drive gear on a drive shaft driven by a drive source in saiddrive system, and wherein each end plate meshes with its own dedicateddrive gear coaxially mounted on said drive shaft.
 54. The bridgingdevice as set forth in claim 53, wherein said interjoined beams are ofdifferent lengths so as to create a trapezium shaped bridging surface.55. The bridging device as set forth in claim 53, wherein saidinterjoined beams are of the same length to create a rectangularbridging surface.
 56. The bridging device as set forth in claim 53,wherein said housing is mounted so as to be capable of tilting relativeto said first point, and wherein said housing further comprising asensor that senses the required angle of tilt such that the tilt anglecan be adjusted.
 57. The bridging device as set forth in claim 53,wherein said housing further comprising an end pull for stabilizing thelast end plates which remain inside said housing when said bridgingdevice is fully extended.
 58. The bridging device as set forth in claim57, wherein said end pull pulls a leading edge of the last end platesdownwards.
 59. The bridging device as set forth in claim 58, whereinsaid end pull comprises a tension spring located horizontally betweenthe last end plates, and a tether attached to each end of said tensionspring which extends in opposite directions, turns through 90° aroundguide rollers and extends upwards to each attach to the last end plates.60. A method of bridging two points comprising the steps of: providing abridging device comprising a housing mountable to a first point; atleast two interjoined beams housed in a retracted position in saidhousing; and a drive system adapted to drive said beams to slide oneover the other to telescopically extend out of said housing from theretracted position to an extended position to thereby form a bridgingsurface to a second point; mounting said bridging device at said firstpoint; and driving said drive system of said bridging device totelescopically extend said beams out of said housing from a retractedposition to an extended position to thereby form a bridging surface to asecond point.